BULLETIN OF THE UNIVERSITY OF WISCONSIN
SCIENCE SERIES, VOL 1, No. 4, PP. 109-156, PLS. 4-8.
A CONTRIBUTION TO THE MINERALOGY OF
WILLIAM HERBERT HOBBS
Assistant Professor of Mineralogy and Petrology
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BULLETIN OF THE UNIVERSITY OF WISCONSIN
SCIENCE SERIES, VOL 1, No. 4, pp. 1O9-156, PLS. 4-8, JUNE, 1895
A CONTRIBUTION TO THE MINERALOGY OF
BY WILLIAM HERBERT HOB
Assistant Professor of Mineralogy and Pet
The crystallized minerals from the pre-Silurian formations of south-
ern Wisconsin: quartz from the Upper Huronian Quartzite of Devil's
Lake; arsenopyrite in dike rock at Marquette; calcite from the Madison
Sandstone (Cambrian) at Madison.
The crystallized minerals from the cavities of the Galena Limestone
in southern Wisconsin.
Calcite from Mineral Point, Linden Mine, etc.
Smithsonite from Mineral Point.
Galena from Mineral Point, Yellowstone, Highland, G a le na
Cerussite from Highland, Mineral Point, and Galena.
Sphalerite from Shullsburg, Mineral Point, and Galena.
Gypsum from Mineral Point.
Barite from Linden Mine.
Marcasite from Linden Mine, Crow Branch Mine, Mineral Point,
Diamond Grove, Hazel Green, Galena, etc.
Pyrite from Shullsburg and Mineral Point.
Azurite from Mineral Point.
Malachite from Mineral Point.
The Druse Minerals from the Hamilton Cement Rock at Milwaukee:
calcite, pyrite, sphalerite, marcasite, celestite, millerite.
Diamonds from the Drift.
So far as I am able to determine, nothing has been pub-
lished descriptive of the crystallography of Wisconsin
minerals. The minerals of economic importance have re-
ilRead before the Wisconsin Academy of Sciences, Arts, and Letters, June 8th, 1895.
110 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
ceived attention, and the minerals in association with
them have been mentioned in the several reports of the
Wisconsin Geological Survey as well as in other publica-
tions. The present investigation has been devoted chiefly
to the crystallographical development of Wisconsin min-
erals, and it has shown that from a purely scientific stand-
point they possess considerable interest. Most of the
species described have been before reported from the lo-
calities, and some, such as the calcites and smithsonites
from the Galena Limestone, are quite widely distributed
in cabinets. A few of the occurrences are quite new. The
list of species considered includes with but few exceptions,
it is believed, all that have been reported as occurring
in definite megascopic crystals within the boundaries of
The material on which this study has been made is chiefly
from the Mineral Collection of the University of Wisconsin,
in which is included the W. T. Henry collection, with little
doubt the most complete collection of minerals that has
been made from the mining region of southern Wisconsin.
The writer is under obligations to Professor Edward
Kremers of the University, for specimens of crystallized
minerals collected from the Hamilton Cement Rock at
Milwaukee, and to Mr. L. S. Cheney, also of the faculty of
the University, for specimens from the vicinity of Platte-
Below is given a partial list of the papers which treat of
Wisconsin minerals. I have not included in this list the
voluminous literature by Irving, Van Hise, Pumpelly,
Brooks, and others, on the crystalline rocks of northern
Wisconsin, in which descriptions of microscopic rock con-
stituents are given.
Moses Strong, Geology and Topography of the Lead
Region. Geology of Wisconsin, Vol. II, pp. 689-752. (1878.)
R. D. Irving, The Mineral Resources of Wisconsin.
Trans. Am. Inst. Min. Eng., New York Meeting, 1880,
pp. 1-31. (1880.)
HOBBS MINERALOGY OF WISCONSIN. Ill
T. C. Chamberlin, The Ore Deposits of Southwestern
Wisconsin. Geology of Wisconsin, Vol. IV, pp. 377-398.
R. I). Irving, Minerals of Wisconsin. Ibidem, Vol. I r
pp. 309-339. (1883.)
George F. Kunz, (Note on finding of Eagle Diamond).
Mineral Resources of the United States for 1883 and 1884,
p. 732. (1885.)
George F. Kunz, On the Occurrence of Diamonds in Wis-
consin. Bull. Geol. Soc. Am., Vol. 2, pp. 638, 639. (1891.)
E. S. Dana, Catalogue of American Localities of Min-
erals. System of Mineralogy, 6th Ed., p. 1087. (1892.)
Wm. P. Blake, The Mineral Deposits of Southwest Wis-
consin. Trans. Am. Inst. Min. Eng., Chicago Meeting,
pp. 1-11. (1893.)
Wm. H. Hobbs, On a recent Diamond Find in Wisconsin
and on the Probable Source of this and other Wisconsin
Diamonds. American Geologist, Vol. XIV, pp. 31-35.
THE CRYSTALLIZED MINERALS FROM THE PRE-SILURIAN
FORMATIONS OF SOUTHERN WISCONSIN.
Quartz Crystals from DevWs Lake. The fissures in the
Upper Huronian Quartzite of Devil's Lake, near Baraboo,
are frequently found to be lined with crystals of quartz,
which though quite small are very clear and have faces
well fitted for measurement. The occurrence of crystallized
quartz in the vicinity of Devil's Lake has been mentioned
by Irving in a paper entitled "Minerals of Wisconsin." 1
These crystals are fully as limpid as the well known quartzes
from Herkimer county, New York. A cry stall ographic
study has been made of them on material recently collected
at Devil's Lake by Professor Van Hise. The crystals have
an average length of 3-6 mm and a thickness of 1-2 mm -
They have generally a marked trigonal habit occasioned by
the unequal development of alternate faces of the prism,
and by the subordination of the form z to r. 2 Besides the
1 Geology of Wisconsin, Vol. I, p. 318, 1883.
2 Throughout this paper the lettering of known planes agrees with that used by Dana in
the 6th edition of the System of Mineralogy. In one or two cases the lettering used by
BULLETIN OF THE UNIVERSITY OF WISCONSIN.
usual forms m, r, and z, the crystals are modified by the
trigonal pyramids s and s', the right and left forms being
often observed together on the crystal. Examination with
a lens reveals the fact that some crystals are further
modified by the occurrence of a positive right trapezohe-
dron between s and z. Measurement with the goniometer
shows this plane to be the form *" 4) -f fpf r> (7187), which
I think has not before been observed, though the comple-
mentary negative left form ^ 4 , IP? 1, (1787) is given in
the lists of Dana and Goldschmidt. In the zone of mr on
another crystal a faint but distinct reflection was also ob-
tained from a plane which has the symbol fR, (47. 0. 47. 30)
and which has not before been described on quartz. The
habit and development of the crystals is represented in
FIG. 1. QUARTZ CRYSTALS FROM DEVIL'S LAKE.
The following list gives the forms observed in the order
of their amounts of development:
m, ooR, (1010).
r, R, (1011).
z, -R, (0111).
s, -- r, (1121).
*', 1, (Sll).
*" 4 , + fPf r, (7187).*
a, tfR, (47. 0. 47. 30).
Irby and Goldschmidt has been adopted. For new planes discovered German letters have
been used wherever this is possible.
HOBBS MINERALOGY OF WISCONSIN.
The angles were measured on two crystals with the fol-
m s, . 1010
S r' 4> 1121
r\ Z, 7187
r\ m, 7187
r z, 1011
r s, 1011
m r, 1010
m a, 1010
47. 0. 47. 30
m m, 1010
The considerable variation from the theory in the meas-
urement fo the angle rz is due to the vicinal character of
the face z. With this exception the faces gave excellent
images of the signal.
Arsenopyrite in dike rock at Marquette, Green Lake County.
This mineral is found as an accessory constituent in a
diabasic rock which occurs in a small dike in Marquette,
Green Lake county. The locality is on the south side of
the hill south of Mr. Ingalls's house and about one and one-
fourth miles south-southwest of the village of Marquette.
FIG. 2. ARSENOPYRITE FROM MARQUETTE.
The mineral occurs in crystals three to four millimetres
across and bounded by the forms u, iPoo (014) and m, ooP,
(110) (See Fig. 2). The u faces are as usual striated par-
allel to their intersection. The faces are all bright and
reflect well, but are too much rounded to admit of measure-
ment Heated on charcoal in the oxidizing and reducing
flames of the blowpipe, arsenic and sulphur fumes are
114 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
evolved and the iron is oxidized. The mineral is locally
supposed to be silver and the locality is referred to as the
Crystallized Galcitefrom Madison. In the extensive quarries
in calcareous sandstone which are located just west of the
city of Madison and which belong to the Lower Magnesian
formation, are occasionally found druse crystals of calcite.
A specimen collected from this locality exhibits crystals of
three to four milimetres diameter lining a small cavity.
FIG. 3. CALCITE FROM MADISON.
These crystals have a yellowish tint and are somewhat
translucent. The faces are considerably rounded, so as to
be unfit for measurement, but the forms can be easily de-
termined to be R (0112) and R (lOlO), the latter very
small. Another specimen is made up of crystals vary-
ing from 1-2 cm in diameter bounded by the form R.
Still another is bounded by R, ooR and a scalenohedron.
Still another specimen, apparently dropped on the Univer-
sity Drive by the quarry teams, is bounded by OP, R, R,
THE CRYSTALLIZED MINERALS FROM THE CAVITIES IN THE
GALENA LIMESTONE OF SOUTHERN WISCONSIN.
The lead and zinc ore region of the Upper Mississippi
valley includes portions of Wisconsin, Illinois, Iowa, and
Missouri. In Wisconsin the mines are now worked chiefly
for zinc, which is obtained very largely from a porous va-
riety of smithsonite colored brown by limonite, and known
locally as dry bone or dry bone ore. This material is mainly
utilized for the manufacture of zinc paint. At Shullsburg,
where there is at present the greatest activity, black jack
is the principal ore and is mined for spelter. The minerals
HOBBS MINERALOGY OF WISCONSIN. 115
associated in the deposits in the Wisconsin area are cal-
cite, smithsonite, galena, cerussite, sphalerite, gypsum,
barite, marcasite, pyrite, chalcopyrite, azurite, malachite,
and limonite. Hematite, siderite, pyrolusite, hydrozincite,
and anglesite have also been reported. As will be shown
below it is probable that what has been reported as angle-
site is a well crystallized variety of gypsum, or selenite.
Some additional minerals, notably amethystine quartz and
calamine, are found in the areas of adjoining states, the
so-called "calamine" of the Wisconsin mines is, however,
not calamine but smithsonite.
Wisconsin calcites, smithsonite pseudomorphs, and azu-
rites, are somewhat widely distributed in cabinets, as are also
the galenas from Galena, 111., but I am not aware that any
crystallographical study has heretofore been made on any
of these minerals.
CALCITE FROM MINERAL, POINT, LINDEN MINE, MIFFLJN,
Southern Wisconsin has long been known as a locality
for crystallized calcite, and specimens from the region are,
therefore, somewhat widely distributed in collections. The
best crystals come from the Linden Mine, Mineral Point,
Galena, and Mifflin. They are frequently found to be modi-
fied, and they show considerable variety in their habits.
Without regarding the less important variations, seven
distinct types of crystal are observed, four of which are
frequently met with and stand in an interesting relation-
ship to one another as regards their periods of formation.
These types may be distinguished as follows: .
Type 1. Habit, common scalenohedron R 3 (2131) very
much rounded ; modified by R and by other undeterminable
faces; color, milk white, brown, or pink, often variegated;
opaque; crystals seldom over two inches in length, though
larger cleavage pieces are found. Linden Mine and Ga-
lena. (See plate 4, fig. 1.)
116 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
Type 2a. Habit, scalenohedron R 3 (2131) quite alone;
color, light wine yellow; translucent to transparent; crys-
tals almost always formed about a nucleal crystal of
type 1; uniformly from three to six inches long; faces
covered by Aetzhiigel due to much corrosion by solvents.
Mineral Point. (See plate 4, fig. 2a.)
Type #&. Habit, fiat rhombohedron JR (0112) either
quite alone or with small face of R (1011); color like
type 2a; translucent to transparent; faces quite free from
etching phenomena ; crystals from three to five inches broad ;
found generally in geodes which have a diameter of a foot or
less. (These crystals were probably formed by the same
solutions as those of type 2a, the difference in habit being
explained by local conditions.) Mineral Point. (See plate
4, fig. 2b.)
Type 3. " Dog tooth spar. " Habit, common scalenohe-
dron R 3 (2131) with moderate truncation by the fundamental
rhombohedron R (1011) and much modified; color, grayish
white; poorly translucent; faces marked by Aetzfiguren and
Aetzkandle but generally without Aetzhrtgel, hence less cor-
roded than crystals of type 2a; usually has a core of type
2a within which is a core of type 1; two sizes of crystals,
about two inches and four to seven inches long respec-
tively. Linden Mine and Galena. (See plate 4, fig. 3.)
Type 4. " Nail head spar. " Habit, fundamental rhom-
bohedron R (1011) moderately beveled by the common scal-
enohedron R 3 (2131) and much modified, the forms being
the same as on crystals of type 3; color, like type 3 but
considerably more translucent, being in this respect inter-
mediate between types 2a and 3; less marked by etchings
than type 3; occurs either alone or as parallel growths on
surface of crystals of type 3, forming knobby projections
if attached to the lateral faces, and scepter calcite resem-
bling "scepter quartz" if attached to the apex of the crys-
tals; when large numbers of these crystals are attached to
the faces of crystals of type 3 they may unite as sub-indi-
HOBBS MINERALOGY OF WISCONSIN. 117
viduals to form apparent secondary enlargements to that
type; usually one to two inches in diameter; Galena, Lin-
den Mine, Mineral Point, and Mifflin. (See plate 4, fig. 4;
also plate 5, fig. 1.)
Type 5. Habit, a combination of the common rhombohe-
dron R (1011), with the basal pinacoid, Of* (0001), and with
small development of R 3 (2131). The only representative
specimens of this type are large twinned crystals which
will be fully described below. Linden Mine. (See plate 4,
Type 6. Habit, prismatic from development of steep
rhombohedron 24R. (188.8.131.52); terminal planes e, v, and
subordinate fc; white and opaque; Diamond Grove. Only
one crystal of this type has been observed. (See plate 4,
Crystallographically the most interest attaches to the
types 3 and 4, since the crystals of type 1 are too much
rounded to permit of any determination of their forms, and
both varieties of type 2 are very simple, 2a exhibiting only
the form R 3 (2131) and 2b the forms R (0112) and R (lOll).
Although the crystals of types 3 and 4 are markedly dif-
ferent in their habits, between which no transitional forms
have been observed, they are identical in their modifica-
tion. The crystals of the latter type being less corroded,
are best suited to measurement, but even on the best of
these crystals the rounding of some of the faces renders
very accurate measurements impossible. They are also
too large for convenience of measuring with the reflecting
goniometer. The following forms have been determined,
those marked with an asterisk being so far as I know new
to the species. They are not included in the lists of forms
compiled by Irby, 1 Goldschmidt, 2 and Dana. 3
1 Irby, On the crystallography of calcite. Inaug. Diss. Gottingen, 1878.
2 Goldschmidt, Index der Krystallformen, I. Berlin, 1886.
3 Dana, E. S., System of Mineralogy, 6thEkU..Sejy. York, 1892.
BULLETIN OF THE UNIVERSITY OF WISCONSIN.
r, R (1011).
e, iR (0112).
v, R 3 (2131).
a, HR (O.ll.n.20).*
b, HR (0.18.18.25).*
/, -2R (0221).
c, 24R (184.108.40.206).*
8, 10R (10.0.10.1).
fc, IR (5052).
S3, 1 |R2 (1123).
f, 1R3 (2134).
57, l ffif (5279).
^, ffif (4156).
These forms have been determined by the following
measurements which are for the most part averages of
several readings made on corresponding angles 2 :
Zone of e and m.
e : a,
e : fc,
e : c,
X), 2131 :
Z), 2131 :
1 Numbers used by Irby.
2 The vicinal character of r prevented measurement, but the plane is easily identified by
the cleavage. The face k is determined by its zones.
HOBBS MINERALOGY OF WISCONSIN. 119
The different forms show considerable difference in
the character of their markings. The planes of R 3 are
striated parallel to their combination edge with R. Both
R 3 and R are often marked by Aetzkanale which incline to
follow the direction of cleavage. On R the etched figures
have the symmetry and approximately the shape of the
artificial figures produced by the action of hydrochloric
acid. This face is very frequently vicinal, the facets rep-
resenting two scalenohedrons of large indices. Between
R and R 3 a small and undeterminable face occurs which is
probably the result of corrosion Prcirosionsflache of Ham-
berg. The new form a, MR (0.18. 18. 25) may possibly
also be of this character.
The parallel growths of four of the different types of
crystals with one another demonstrate the fact that they
represent successive separations from the solutions from
which they were formed, their order of age being that rep-
resented by the numerals assigned to the types, viz. : 1, 2a,
3, 4, type 1 being the oldest. The crystals of type 2b
were probably formed at the same time as those of type
2a, bat in a different situation. Crystals of type 1, though
common as a core of the later types, are most rarely found
alone. The crystals of type 2a were most easily corroded
by solutions, for specimens of parallel growths with the
two later types are found in which the core of type 2 has
been entirely removed, whereas the enclosing zone of type
3 has only been rendered porous and that of type 4 has been
comparatively little affected. In one instance the cavity
left by the removal of type 2 has been filled with sphal-
erite, thus forming a mechanical infiltration pseudomorph.
Numerous specimens in the University Collection are
parallel growths of the four types in isomorphous layers,
and when broken across these types are seen to be sharply
separated from one another by the differences in color and
transparency. A few parallel growths include less than
the full series of types, but no one of the types has been
120 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
observed out of the order stated. The character of one of
these interesting parallel growths is represented in plate
5, fig. 1.
The only representative specimens of type 5 are two
large twinned crystals from the Linden Mine. They are
interesting both because they are the only specimens in the
collection on which I have observed the basal pinacoid, and
because they furnish the only observed illustration of twin-
ning in the calcites of the region. The specimens are very
large (the largest about 7x6x5 inches), and have a gray
color and a much corroded surface. The individuals of
both specimens exhibit the combination of the fundamental
rhombohedron, R (1011), with the basal pinacoid, OP (0001)
and the common scalenohedron, R 3 (2131). On one of the
individuals of the larger specimen the basal plane has a
very large development influencing the habit of the crystal,
while on the other individual it is quite small. The two
individuals have parallel axes, and the twinning plane may
be considered either a face of the fundamental prism, ooP
(1010), or the basal pinacoid, OP (0001). The large triangu-
lar area of the basal pinacoid on one individual is divided
very accurately into two smaller and perfectly equilateral
triangles by the projection above it of the rhombohedral
faces of the other individual. On the largest of these tri-
angular areas has formed a deep green yellow calcite en-
largement. This addition of calcite material has extended
the rhombohedral planes which outline two sides of the
triangle, and on the third side opposite the rhombohedral
face of the other individual it has developed a new rhom-
bohedral face, so that the apparent lack of symmetry be-
tween the two individuals caused by the greater develop
ment of c on one of them, is in part removed. The other
triangular section of the pinacoid has received no addition
of calcite material. To one side of the specimen are at-
tached small crystals of barite which will be described be-
HOBBS MINERALOGY OF WISCONSIN. 121
The smaller specimen of this type is very similar to the
one just described, but the basal plane has a smaller de-
velopment, and on one individual it hardly appears at
all. It is interesting, however, to note that there has been
an addition of the yellow green calcite to this plane, so as
to extend the surrounding rhombohedral faces and replace
the pinacoid in the manner described for the first specimen.
The stereographic projection (plate 5, fig. 2) represents
all the forms observed on the caicites of this region and
exhibits their zonal relationships.
SMITHSONITE FROM MINERAL POINT.
The mineral smithsonite occurs at Mineral Point in two
forms, one a massive, semi-vitreous, white to gray variety,
locally called "calamine, " which incrusts much of the cal-
cite and blende of the locality, and the other a porous
gray to brown variety known as "dry bone," apparently in
all cases a replacement pseudomorph after either calcite
or blende. The "dry bone" variety is much the more
abundant. The more perfect pseudomorphs after caicite
are very beautiful and represent the types 3 and 4 described
under calcite. As these pseudomorphs are well known and
are somewhat widely distributed in cabinets, a full descrip-
tion of them here is unnecessary. They have evidently
been produced through the action of solutions by a metaso-
matic process of alteration, the lime of the calcite being
replaced molecule by molecule by zinc. An examination of
the wide range of specimens in the University Collection
shows, however, that there have generally been several
stages in the process. In most cases the first change was
an incrusting of the calcite crystals by the compact "cala-
mine" variety of smithsonite. As a result of this nearly
all the pseudomorphs have an outer shell of compact ma-
terial. The second stage of the process consisted in a
partial, and in some cases even a complete, solution of the
included calcite crystal. This solution if partial, as was
122 BULLETIN OF THE UNIVERSITY OP WISCONSIN.
generally the case, took place along the cleavage cracks
parallel to the rhombohedron, thus separating the crystal
into partially detached rhombic blocks. Along the chan-
nels thus opened the solutions which effected the change
found their way and replaced molecule by molecule the
residual blocks, the channels remaining unfilled in the
Numerous specimens in the University Collection indi-
cate that the process above described was in some cases
varied by the complete solution of the calcite and the fail-
ure to refill the cavity. Very beautiful incrustation pseu-
domorphs have resulted in this way. The majority of the
specimens, however, contain residual portions of unaltered
calcite, and clearly indicate that in most cases all stages of
the process went on simultaneously in different parts of
the crystal, the action beginning at the surface immedi-
ately under the incrustation of the "calamine" variety.
FIG. 4. SMITHSONITE PSEUDOMORPH AFTER CALCITE, FROM MINERAL POINT.
Such specimens have immediately beneath the incrustation,
a layer of the porous "dry bone" retaining the cleavage
channels of the calcite. This layer is sharply delimited from
the incrustation, but passes insensibly into the layer of
porous corroded calcite immediately beneath, which like-
wise passes by all intermediate phases into the unaffected
calcite nearer the center of the crystal. (See figure 4).
The dry bone material of these pseudomorphs is invari-
HOBBS .MINERALOGY OP WISCONSIN. 123
ably colored ochre yellow by limonite in the pulverulent
form, and this material is sometimes found quite pure. Its
fine state of subdivision as well as its uniform distribution
in the pseudomorphs, makes it probable that its source is
the iron of the "black jack" which supplied the zinc to the
solutions, as has already been pointed out by Chamberlin. 1
The pseudomorphs of smithsonite after sphalerite which
are in the collection are of much less interest, since they
have the form simply of plates and spheroidal masses and
not of definite crystals of blende. 2
GALENA FROM YELLOWSTONE, MINERAL POINT, HIGHLAND,
The crystals of Galena from this region are invariably
either cubes or a combination of the octahedron and cube.
On some specimens from Galena the rhombic dodecahedron
occurs as a small truncation of either the cubic or the octa-
hedral edge. The largest crystals come from the Yellow-
stone Diggings. The Yellowstone crystals are always
elongated, either in the direction of a principal axis, which
produces an apparently tetragonal combination (see
plate 6, fig. 2), or in the direction of a digonal axis,
which results in an apparently hexagonal combination
(plate 6, fig. 1). The length of these apparently prismatic
crystals may be several times their breadth. A crystal of
tetragonal habit in the University Collection has a length
of over a foot and a breadth and thickness of about four
inches. Another crystal with hexagonal habit is about
nine inches in length with transverse dimensions of about
four inches. The faces of these crystals are considerably
rounded from corrosion. The specimens which come from
Highland are quite symmetrical cubes with the cubic edge
1 T. C. Chamberlin. The ore deposits of southwestern Wisconsin. Geology of Wiscon-
sin, Vol. IV, p. 396. (1882.)
2 Dana states in his system (6th ed.) that pseudomorphs after crystals three inches or so
in diameter are found at Mineral Point. None are, however, contained in the University
124 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
often as much as three inches in length. A specimen from
Benton presents interesting skeleton growths, which out-
line the half of an octahedron truncated by a cube. This
probably represents one phase of the Galena referred to
as reticulated galena in the report of the state geologist. 1
The more beautiful feather-like skeleton growths have been
figured in that report.
FIG. 5. AGGREGATE OF GALENA FROM MINERAL POINT.
At Mineral Point have been found large quite symmet-
rical cubes resembling those found at Highland. On some
specimens the faces of the galenas are studded with octa-
hedrons of pyrite which are superficially altered to limon-
nite. On the crystals of other specimens are found gray
cerussite crystals from 5-7 mm in diameter. Still another
series of specimens from Mineral Point presents very beau-
tiful aggregations of sub-individuals on which the octahe-
dron has a large development, forming hopper faced aggre-
gate individuals of the same habit (see figure 5). The
average size of the component individuals is only a few
millimeters and they are nearly perfect carbo-octahedrons,
but at the ends of each of the principal axes of the aggre-
gate crystal are large crystals with cubic habit, whose
cubic face determines the size of the cube face on the ag-
gregate crystal. The aggregate crystals have quite uni-
formly a diameter of about three to six centimeters and
i Chamberlin, Geol. of Wis., Vol. IV. p. 385. (1882.)
HOBBS MINERALOGY OF WISCONSIN. 125
the component individuals at the ends of the principal
axes a diameter of about one to two centimeters.
On specimens from Highland are found interesting arbo-
rescent forms not unlike the forms assumed by native cop-
per (see figure 6). The individual cubes are much elongated
in the direction of a principal axis and otherwise distorted,
and the arborescent groups of crystals are often attached
by the end of a single crystal, so that their resemblance to
trees is very striking.
FIG. 6. ARBORESCENT FORM OP GALENA FROM HIGHLAND.
Polysynthetic twin lamellae like those described by
Cross l have been observed on crystals from several of these
localities. On crystals from Highland the twinning plane
of the lamellae is the octahedron, which corresponds to the
second law mentioned by Cross. The crystals on which
the lamellae are observed, are cubes with small trunca-
tion by the octahedron. The faces of the cube are divided
along lines parallel to their own edges into four sectors,
in each of which pronounced striations run parallel to the
adjacent octahedral face. All the cubic faces are affected
in the same manner, but the octahedral faces are quite
plane. This structure is indicated in plate 6, fig. 7.
Lamellar twinning according to the other law deter-
mined by Cross, where the twinning plane is a plane of
the dodecahedron, is well shown by crystals from Mineral
Point. The appearance of these crystals is shown in plate
1 Whitman Cross, Note on Slipping Planes and Lamellar Twinning in Galena. Proc
Col. Sci. Soc., 2, p. 171-174 C1887).
126 BULLETIN OF THE UNIVERSITY OP WISCONSIN.
6, fig. 6, which has been drawn from one of the crystals
examined. The top cubic face of this individual is stri-
ated in the same manner as the crystals from Highland,
but the structure is different on the adjacent faces. Here
the course of the lamellae is parallel to the cleavage lines,
showing clearly that the twinning plane is the dodecahe-
dron. On one of these faces a division of the face into
sectors is noticed, but in this case the lines of division run
parallel to the diagonals of the face. A few of the stri-
ations take their course across the direction of the pre-
vailing ones at such an angle as to suggest that they rep-
resent a third law of twinning for the mineral such as has
been described by Sadebeck, 2 in which the twinning plane
is a trisoctahedron. In all cases the sectors into which
the striations divide the faces constitute vicinal planes, all
of which slope away from the center of the face.*
An exceptionally beautiful instance of the dodecahedral
twinning above described is afforded by a large crystal
from Yellowstone. This specimen is the broken end of
what was apparently one of the elongated crystals with
tetragonal habit which are common from this locality. The
crystal had a breadth of about five and a thickness of some
four centimeters. Figures 3, 4, and 5 of plate 6, repre-
sent three parallel sections of this crystal along the cleav-
age planes, those of figures 4 and 5 being separated by
about three centimeters and those of figures 3 and 4 by
about a centimeter and a half. The central portion of the
a Zeitsch. d. D. geol. Gesellsch., Vol. XXVI, p. 631 (1874).
*NOTK. That these twin lamellae have been noticed before on Galena from the upper
Mississippi valley, is evident from the following extract from a paper by James T. Hodge
entitled, "On the Wisconsin and Missouri Lead Region," which was published in Silliman's
Journal in 1842 (Vol.43, p. 38):
" The smelters think they can distinguish the ores that are found in different fissures
that from an east and west fissure being perfectly crystallized, of a smooth surface, striae
indistinct; that from a north and south fissure, of crystalline structure, with two sets of
striae very distinct, crossing each other at right angles; and the ore from a quartering fis-
sure crystalline, with many sets of striae crossing each other obliquely; and to some ex-
tent I had opportunity of proving their observations correct."
Supposing this idea of the smelters to be correct, it is difficult to account for this differ-
ence unless the crystals of galena have a uniform orientation with reference to the walls
of the fissure.
HOBBS MINERALOGY OF WISCONSIN. 127
crystal is an unstriated nucleus whose former crystal
boundaries are indicated by a line of tarnished mineral.
The nucleus contains irregular-shaped cavities in which
cerussite has crystallized. The striations in the outer por-
tion of the crystal are high ridges near the periphery, but
these diminish in prominence as they take their course to-
ward the nucleus, dying out completely before they reach
it, and as they do so often taking a sharp curve to a di-
rection which suggests a sudden change to the law of
Sadebeck. It is evident that this structure has not been
produced by any stress to which the crystal has been sub-
jected since its formation, but it is in some way to be con-
nected with the strains induced in the outer portion of the
crystal, as it accommodated itself to the nucleal crystal in
growing about this and being oriented by it. Lamellse
have also been observed on crystals from Platteville, Wis.
Some very interesting forms of galena come from Galena,
111. Many specimens indicate that there have been for the
limestone cavities at least two periods in which galena crys-
tallized out, separated by a period when crystallized marca-
site was deposited. Cubes of galena, having an edge of
three to five centimeters, are found coated with marcasite
and studded with numerous nearly perfect octahedrons of
galena, having a diameter of about two millimeters. The
octahedron is usually absent from the crystals of the first
separation of galena though it sometimes appears as a very
minute truncation of the solid angles; while the cube,
though always very small, is usually present on the octa-
hedral crystals of the later generation.
One crystal in the collection has some interest from its
twisted form. It is a simple cube elongated in the direc-
tion of a principal axis so that its length is about six inches
and its breadth and thickness only about two inches. One
end of the crystal is nearly or quite parallel to the other but
occupies the position it would have if it had been rotated
thirty degrees from its normal position about the long
128 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
axis of the crystal. The long faces of the crystal present
a nearly perfect warped surface with only a single impor-
tant interruption near one end.
On closer examination very slight interruptions are no-
ticed at intervals of three or four centimeters, which indi-
cate that the apparent individual is an aggregate of sev-
eral individuals nearly, though not quite, parallel. Each
individual is rotated through a small angle from its nearest
neighbors about the axis of the aggregate, the rotation
being always in the same direction. But this is not the
only attempt which the crystal has made to assume a spiral
form, for the faces of the sub-individuals are warped, and
though the greater part of the aggregate is coated with
marcasite, a cleavage surface is exposed at one point and
exhibits the polysynthetic twin lamellae. It is thus prob-
able that the crystal has been subjected to some force from
without which has inclined it to the direction it has taken.
CERUSSITE FROM HIGHLAND, MINERAL POINT, AND GALENA.
This mineral always appears on the surface of Galena
crystals where it has doubtless been formed through the
action of carbonated waters. The best specimens in the
University Collection were found at Highland and Mineral
Point. Larger but less perfect crystals are common on
specimens from Mineral Point and from Galena, 111., the
latter place being located but a few miles from the state
boundary. The Galena to which the Highland cerussite is
attached occurs on the hopper-faced octahedrons composed
of a great number of sub-individuals, which have been de-
scribed under Galena (Fig. 5). Two strikingly dif-
ferent types of Cerussite crystals are found upon the
same specimens, the one being long columnar in the direc-
tion of the brachydiagonal axis, and the other pseudo-
hexagonal in habit, from the nearly equal development of
pyramid and brachydome. Both types are to be found in
HOBBS MINERALOGY OF WISCONSIN.
twins according to the common law, the twinning plane a
face of the fundamental prism. Stellate forms of the sec-
ond type are frequently only to be distinguished from the
individual crystals by a search for the twinning lines, or by
measurement of the angles on the goniometer.
Type 1. Crystals columnar in the direction of the brachy-
diagonal axis: Crystals of this type usually have a length
several times their breadth, and have their habit condi-
tioned by the brachy domes i (021) and x (012), and the pyra-
mid p (111) (see plate 7, fig. 1). They vary from four to
eight millimetres in length. The forms observed upon
them are the following, y being new to the species:
i, 2Poo (021).
x, iPoo (012).
y, -Poo (0.25.4).*
P, P (HI).
b, ooPoo (010).
m, ooP (110).
r, ooP3 (130).
The above enumerated forms were determined by means
of the following measurements :
62 46' 62 46'
57 35 57 19
58 37 58 42
35 46 35 46
69 13 69 20
39 51 39 45
34 31 34 40
12 304- 12 29
i' t 010
130 BULLETIN OF THE UNIVERSITY OF WISCONSIN
The face y is certainly (0.25.4) and not the known form
(061), as the face is a large one and quite perfect. Both
y and & reflect finely, giving single sharp images of the
signal. The calculated angle & : t (010 : 061), is 12 59',
which differs from the value obtained by over 18', whereas
it is impossible that an error of more than a very few min-
utes should be made in the reading. With the exception
of r, which is small and gives only a faint reflection of the
signal, all the faces afford excellent readings.
Type 2. Crystals with pseudo-hexagonal habit due to the
nearly equal development oj the pyramid and brachydome: The
individuals of this type (plate 7, fig. 2) are generally larger
than the crystals of the first type and have the habit of the
crystals from Berezov figured by Dana, ' but they are more
modified. Their habit is conditioned chiefly by the forms
p, -i, and &. They may be easily confused with stellate
twins, which occur with them and from which they can
often only be distinguished by a measurement of the angles
in the prismatic zone, the angle m : m being either 54 28'
or 62 46', while that of m : b is 58 37'. Most of the
crystals are twinned at least once, the twinning line taking
usually a somewhat irregular course over the faces and
frequently bringing p and i nearly into coincidence. On
single individuals the faces are all remarkably perfect and
give each a single sharp bright image of the signal. The
forms are as follows: *
P, P (HI)-
m, ooP (110).
a, ooPoo (100).
&, ooPoo (010).
i, 2Pao (021).
k, Poo (Oil).
x t tPao (012).
' System, 6th ed., p. 287, fig. 8.
HOBBS MINERALOGY OF WISCONSIN.
The following measurements were made to identify the
On twinned individuals:
m : m, 110 : 110
Many of the crystals have their faces studded with nu-
merous small lenticular yellow crystals with much rounded
faces, which are probably siderite.
The best cerussites which I have examined from Mineral
Point are found, like the Highland crystals, on skeleton
octahedrons of galena. Some of the smaller crystals have
very sharp faces, and so far as examined they appear to
have the same forms and habits as the Highland crystals.
Type 3. Crystals wiih domal habit. The large gray cer-
ussites which come from Galena and Mineral Point, are
less perfect and less highly modified than the types just
described. The faces reflect poorly, but the following
goniometer readings were made on crystals bounded by the
forms i, x, m, and subordinate p, this being apparently the
usual habit. (See plate 7, figure 3.)
i : i', 021 : 021
x : x', 012 : 012
m : m', 110 : 110
p : p, (with front lens)
These crystals are as frequently simply twinned as the
Highland crystals. Their form is represented in plate 7,
132 BULLETIN OP THE UNIVERSITY OF WISCONSIN.
fig. 3. An analysis of such crystals on selected material
from Galena yielded Mr. R. B. Green the following
PbO ........................... 83.42 83.52
CO 2 ........................... 16.45 16.48
The material was specially examined for zinc with nega-
SPHALERITE FROM SHULLSBURG, MINERAL POINT, AND
Although sphalerite is one of the most common minerals
in the crevices of the Galena Limestone, it is usually found
in the massive form or in small and imperfect crystals. It
usually contains a small amount of iron sulphide, as is indi-
cated by its dark color. I recently collected at the Wis-
consin Zinc and Lead Company's mine at Shullsburg, some
specimens of this mineral on which the crystal forms can
be made out. These sphalerite crystals occur in an elon-
gated roughly cylindrical cavity, which has been formed by
the solution and removal of a fossil, probably an ortho-
ceras. The largest crystal is over a centimeter in diame-
ter and is a much distorted simple individual on which are
found the following forms :
o, + (111).
d, ocO (110).
I_ 3O3 /Q1
m, + -- (311).
HOBBS MINERALOGY OF WISCONSIN. 133
All the faces with the exception of m are dull and conse-
quently give no image of the signal. The face m is very
bright but is rounded through bevelment by a considerable
number of hexoctahedrons having large indices. The angle
m : m (over a), was measured by reflection and found to be
50 53', the theoretical value being 50 28'. The angle d : d,
(101 : Oil) was roughly measured with a hand goniometer
as 61, the calculated angle being 60. A hexoctahedron
which has a development about equal to m, and whose faces
occur on either side of the m face, could not be determined
owing to the lustreless character of its faces.
A smaller crystal from the same specimen is bounded by
the forms o (111) and d (110) and is twinned according to
the common law for this mineral, the twinning plane a face
of o. Other specimens from Shullsburg are light wine yel-
low in color to nearly colorless and transparent.
An analysis by Mr. E. B. Skinner of the darker crys-
tals first described gave the following :
Sphalerite also occurs in crystals at Platteville and at
Mineral Point, the individuals obtained from the former
locality being a centimeter or more in diameter, while those
from the latter locality are small though often with toler-
ably bright faces. The forms d, o, and m were observed
upon both. Frequently, however, those found at Mineral
Point are coated with a layer of white mineral which is
probably smithsonite. Dana 1 states that crystals of this
mineral three inches or more in diameter are found altered
to smithsonite at Mineral Point. No such specimens are
included in the University collection, though spheroidal ag-
gregates of crystals as large as that are not uncommon,
and these are sometimes altered to smithsonite. No crystals
i System, 6th Ed., p. 62.
134 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
of sphalerite much over a centimeter in diameter have
been observed by the writer on Wisconsin specimens.
Sphalerite is found in exactly the same association at
Galena. These o.rystals have much the same form, but some
have been found on which the faces are much more
perfect. They nearly always exhibit one form in addi-
tion to those observed on crystals from the other localities.
FIG. 7. SPHALERITE FROM GALENA, ILL.
This is the tetragonal tristetrahedron or hemi-trisoctahe-
dron A, 1O (775) which has not, I believe, been before ob-
served on this mineral. On one crystal in particular the
faces d, o, and A are very perfect and give excellent reflec-
tions of the signal (Fig. 7). On this crystal the following
measurements were made:
o : d, 111 : 110 35 18' 35 16'
d : A, 110 : 775 26 49 26 48
On the same crystal the faces of the icositetrahedron
(probably m) and the hexoctahedron are too much rounded
to admit of measurement. On less perfect crystals the
face A was measured with results varying 11' to 12' from
those obtained on the most perfect crystal.
HOBBS MINERALOGY OP WISCONSIN.
GYPSUM FROM MINERAL POINT.
The specimen about to be described was presented to
the ^University Mineral Collection by a friend, who obtained
it from a local collector at Mineral Point. It was sup-
posed to be anglesite by the person who collected it, pos-
sibly because it occurs on crystals of galena . The crys-
tals referred to are long columnar in habit, colorless, and
perfectly transparent. Their greatest length is 10 mm .
and their greatest breadth about 2 mm . They are attached
bo small cubes of galena which are covered by a layer of
red cryptocrystalline smithsonite. As this is an unusual ap-
pearance for the local smithsonite, it was determined to be
that mineral by its reacting for zinc on charcoal and being
completely soluble with effervescence in hydrochloric acid.
The red color of the mineral is superficial, the under por-
tions having the usual gray color.
FIG. 8. SELENITE FROM MINERAL POINT.
The transparent colorless crystals which are attached to
the smithsonite and galena, are not anglesite as supposed,
but gypsum or selenite. They have the usual habit of
gypsum crystals, being bounded by the prism and clino-
pinacoid and the rounded terminal planes, ?, (Ill) and occa-
sionally e, (103) (see fig. 8). The following measurements
BULLETIN OF THE UNIVERSITY OF WISCONSIN.
are the average of a number which were made with the re-
flecting goniometer on several crystals, the rounded char-
acter of the faces sometimes introducing errors of as
much as 30':
m : m (front) 110
m : m (back) 110
m : b (front)
: 6 (back) ]
The terminal faces were too much rounded to permit of
measurement. The clino-pinacoidal cleavage is almost
micaceous in perfection and the pyramidal cleavage (n) is
well developed. There was no case of twinning observed.
The hardness is 2. Ignited on charcoal in RF the powder
of the mineral glows and yields an alkaline residue.
Moistened with hydrochloric acid and introduced into the
flame of the Bunsen burner it shows the calcium flame.
The optical orientation of the mineral was found to agree
in every respect with that of gypsum. Since the examina-
tion of this mineral was made, Prof. Kremers of this uni-
versity has shown me a very similar specimen from Mineral
Point which was brought to him labelled "anglesite. " It
is therefore almost certain that the mineral which has
been referred to as "anglesite" from Mineral Point in the
state reports is really gypsum. These references are al-
ways very indefinite, and usually state that the mineral is
"reported" or is "said to occur" at the locality. No de-
termination of the supposed anglesite seems to have
HOBBS MINERALOGY OF WISCONSIN. 137
BARITE FROM THE LINDEN MINE.
Barite or barytes, as it is called at the mines, has been
found massive in considerable abundance at a number of
localities in the eastern portion of the mining region.
Specimens from Mineral Point, Crow Branch Mine, the
Welsh Settlement in Iowa county, and the Linden Mine,
are included in the University Collection. The mineral is
almost invariably crystalline, as is shown by its cleavage
and by the projection of indeterminable crystal edges from,
its knobby surfaces. Crystals have been reported from
Scale's Mound just over the interstate boundary in Illinois.
I have not been able to examine any specimens from this
locality. A few crystals of the mineral were, however,
found attached to one of the faces of the larger twinned
crystal of calcite from the Linden Mine, which has already
been referred to in this paper. These crystals of barite are
represented in plate 7, figure 4. They have a maximum
length of about a centimeter and a half, are of a light gray
or brown color, and possess a rather unusual habit. They
are lath -shaped, approaching acicular, with the direction of
principal development the macro-diagonal axis. This fact
is easily determined, since the acute angle of the perfect
prismatic cleavage is found at the extremities of the crys-
tals. The narrow tabular plane which forms the top of
the laths is the basal pinacoid, since it is parallel to the best
cleavage. The other planes present are m, ooP (110) and
d, ^Poo (102). The former can be seen to be parallel to
the second cleavage, and the latter has been determined
with sufficient accuracy by the following measurement
made upon the reflecting goniometer, the face c affording
a fair and d a much blurred image of the signal :
c : d, 001 : 101 37 45' 38 51'.
Most of the faces are dull and reflect poorly, but poor
as the measurements are they are the best that were pos-
138 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
sible under the circumstances. Some very imperfect
crystals of barite, in part colored brown by oxide of iron,
have been collected by Mr. L. S. Cheney from Belmont,
MARCASITE FROM LINDEN MINE, CROW BRANCH MINE,
MINERAL POINT, DIAMOND GROVE, HAZEL
GREEN, AND GALENA.
The mineral marcasite is found at many localities in the
Galena limestone, and seems to be of much more common oc-
currence there than pyrite. It appears under a variety of
forms. It is sometimes found as a cryptocrystalline to crys-
talline coating on the surface of galena or blende, and it also
occurs in well formed crystals, the University Collection in-
cluding a good suite of specimens from the several locali-
ties These crystals of marcasite show as great variety in
habit and combination as the massive and cryptocrystal-
line varieties show in their shapes. At least seven differ-
ent types of crystals have been observed on the specimens
in the University Collection. These will be described in
detail below. Their distribution is indicated in the follow-
Type 1. Linden Mine, Crow Branch Mine, and
Type 2. Linden Mine.
Type 3. Diamond Grove.
Type b. Hazel Green.
Type 5. Hazel Green.
Type 6. Galena.
Type 7. Galena.
Type 1. Crystals of this type have a thin tabular habit
and are bounded by the forms c, OP (001); m, ooP (110) ; I,
Poo (Oil), and v, iPoo (013). (See plate 8, fig. 1.) The base
is as usual the plane of tabular development, and the edge
I : I at the extremity of the 6 axis is about as long as the
HOBBS MINERALOGY OF WISCONSIN. 139
face m, so that crystals have a hexagonal appearance when
observed in the direction of the c axis. The specimen
which shows the most perfect crystals of this type is
without a label, but it was obtained from the W. T. Henry
Collection with material from the Linden Mine, and was
probably found at that locality. These crystals have a
diameter of 5-8 raiu . The following measurements were
made upon them :
m : m, 110 : 110, 75 22' 74 55'
I : I, Oil : Oil, 100 5 101 58
The prism m is sometimes beveled for a short distance
by a prism which gives a reading of 78 1', the reflection
of the signal being as sharp and bright as that from m. In
one instance also a brachyprism gave a reading of 99 52'.
These two forms would correspond to the symbols of the
brachyprisms MPoo and f^Poo , but in view of the wide
variations of the angles exhibited by crystals of marcasite,
the correctness of these symbols can not be relied upon.
The face I furnishes but poor images of the signal
and c and v are altogether unsuited to measurement. The
greater number of specimens of this type are parallel
growths, each individual varying slightly from perfect
parallelism with the individuals adjacent. This produces
the usual "cockscomb" forms. Twins, with the twinning
plane the prism m are quite common, but so far as observed
they are composed of but two individuals (plate 8, fig. la).
On one such twin the angle between adjacent prism faces
lying on either side of the twinning plane was measured
with the following result :
m : m, 110 : 110, 30 1' 30 10'
Pseudomorphs of limonite after marcasite have been
found at Mineral Point as well as at other localities. Ex-
140 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
cellent specimens from Mineral Point are included in the
Type 2. On some specimens from the Linden Mine the
marcasite crystals have a lath- shaped habit due to their un-
usual development in the direction of the & axis, the macro-
pinacoid forming the edge of the lath, c the fairly broad
top, while the brachy domes at the top and bottom and m
from the vertical faces, produce a slight sharpening of the
laths at the ends (plate 8, fig. 2). All the faces are very
much curved and can not be measured. It is noticeable that
the prism is connected to the macropinacoid by a uniformly
Type 3. This type of crystals is common on specimens
from Diamond Grove. The crystals are invariably stellate
twins, the individuals composing which have a thick tabu-
lar habit with c small and I large, and are but little striated
or rounded (plate 8, fig. 3). No simple twins were ob-
served, the groups being apparently cyclic fivelings though
the fifth individual is not made out owing to the broad at-
tachment of the twin by one of its edges. The reentrant
angles formed by m appear between individuals, but they
are very small. The face c is striated by oscillatory com-
bination with either I or v. Unlike the crystals of type 1,
which have a brassy lustre, or those of type 2, which have
a greenish color, the surface of these individuals has a
reddish brown color and an iridescence which is ascribed
to incipient alteration to the hydrated oxide. The stellate
groups have a diameter of 3-4 mm . and are attached to green-
ish marcasite which forms a surface layer over blende, its
tabular crystals being oriented normal to the surface of the
blende and crowded so closely that only the edges of I can
Type 4- This type represents the simplest combination,
the only forms developed being c and m (plate 8, fig, 4.).
The individuals are quite thick so that they have rather
the appearance of short prisms with diamond cross sec-
HOBBS MINERALOGY OF WISCONSIN. 141
tion, than of tabular plates. Simple twins with twinning'
plane the prism are common on these specimens. The
prism was determined as m by the following measure-
m : m, 110 : 110, 105 2' 105 5'
On twinned crystals,
m : m, 110 : 110, 30 34' 30 10'
The face c is striated parallel to the brachy diagonal
axis, which causes a slight rounding of the face near the
edge 110 : 110. The color of this type of crystals is
brown. Parallel growths of a simple character produce
the "cockscomb" aggregates.
Type 5. The second type of crystals from Hazel Green
(plate 8, fig. 5) is quite different from the first, but al-
most identical with a marcasite from Schemnitz which is
figured by Dana. 1 These crystals have a diameter of
4-5 mm . and are quite symmetrically developed. They are
bounded by the following forms:
m, ooP (110).
I, Poo (Oil).
e, Pc (101).
s, P (111).
x, mPoo (Olh).
The faces are bright with a brassy lustre and in most
cases reflect but a single image of the signal, so that the
probable error of reading is very small. Notwithstanding
this fact the measurements of corresponding angles not
only vary much from the values determined by Sadebeck
for this mineral but they vary much from one another.
This variation must therefore be explained by actual vari-
ations in the angles themselves, though the faces do not
i System, 6th Ed., p. 95, fig. 2.
142 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
show vicinal planes, and with the exception of I and x are
not striated. The variation in the angles of marcasite is
well known and the values obtained by Sadebeck are not
supposed to be very accurate. The measurements made
on the crystals from Hazel Green are as follows, the gen-
eral correctness of the average determination being con-
firmed by the zone relations:
a : s (over 1) 111 : 111 88 57' 90 48'
s : s (over e) 111 : 111 65 35 66 7
s : s (over m) 111 : 111 56 7 52 28
I : I, Oil : Oil 99 56 ^)
99 13 [ 100 26' 101 58
102 9 )
e : e, 101 : 101 113 48 ^)
112 30 [112 47 116 20
112 3 J
I : x, Oil : Olh 54 16
x : I', Olh : Oil 44 38
Beside the form x, which occurs with only half its
planes on these crystals, the edge II' is occupied by a
large number of indeterminate brachydomes, so that the
edges Ix and xl' are well rounded. If the readings Ix and
Vx could be relied upon the form x would have the sym-
bol iTPoo , and it is in any case a very flat dome. That it
is not the basal pinacoid, which occurs on the Schemnitz
crystals, is apparent even by examination with the naked
eye. A number of simple twins and several poly syn-
thetic trillings were observed on these specimens (plate 8,
fig. 5a). The twinning plane is shown to be m, the unit
prism, by the twinning line following the edge le and then
traversing the face m parallel to the edge mm. Trillings
are easily determined from the zigzag forms assumed by
the x plane.
HOBBS MINERALOGY OF WISCONSIN. 143
Type 6. The crystals of marcasite from Galena which
are in the University Collection bear most resemblance to
the crystals of type 5 from Hazel Green. One variety has
a distinctly prismatic habit conditioned by the large devel-
opment of the prism m, the nearly equal development of
the domes I and e, and the absence of the base c, the dome
x, and the pyramid s. Crystals of this type are built up of
a large number of sub -individuals and are nearly always
twinned with a face of m the twinning plane (plate 8,
fig. 6.). Such twins are either simple twins or polysyn-
thetic trillings, in which latter case the middle individual
is quite thin. A trilling is easily distinguished from a
simple twin by the striations on the I faces. In a simple
twin the larger striated I faces are adjacent, and opposite
to a pair of adjacent and glistening e faces (plate 8,
fig. fib. ). In a trilling two e faces appear opposite one an-
other as in a simple individual (plate 8, fig. 6a), and the
only evidence that the crystal is twinned may be the re-
entrant angle along the edge le and on the face m. Al-
though a majority of the crystals are composed of small
sub- individuals which appear as projections on the faces
of the aggregate crystal, many of the composite individuals
are terminated by one large simply twinned crystal. On
such a twinned individual the following measurements were
I : e, Oil : 101 68 18' 70 49'
e:e, 101 : 101 54 57 56 34
I : I, Oil ;011 84 36 85 4
A specimen of marcasite collected at Galena by Mr.
L. S. Cheney has a somewhat different development. The
fundamental prism is large, giving the crystals their
columnar form, while v, iPoo and subordinate 1, Poo serve
as terminal planes. These crystals are in part attached to
larger octahedrons of pyrite.*
* NOTE. Some quite interesting arborescent aggregates of marcasite crystals were col-
lected by Mr. Cheney at Cuba City, Wis. These were received too late for study in connec-
tion with the other specimens of this mineral which are here described.
144 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
Type 7. Another variety of the Galena marcasite crys-
tals resembles type 5 more closely, though s and m are
both very small. They are frequently attached by one of
the dome faces so that an opportunity is given for the de-
velopment of dome faces at both ends of the crystals. The
result is a mimicry of the octahedron, so that these crys-
tals might be taken for octahedral pyrite having small
truncations by the cube (plate 8, fig. 7). On some speci-
mens radial groupings of such crystals produce aggregates
having a diameter of about two centimeters, on which par-
ticularly large crystals or groups of crystals project at
points corresponding to the ends of the crystallographic
axes, and make the groups somewhat resemble hollow-faced
Dana 1 has figured a crystal from Galena which has a tab-
ular habit, is bounded by the forms Z, v, c, &, m, e, and s, and
is twinned according to m.
PYRITE FROM SHULLSBURG AND MINERAL POINT.
Pyrite, like marcasite, is a common mineral in the crev-
ices of the Galena Limestone. Well crystallized specimens
would not, however, seem to be very common. During a
recent visit to the Wisconsin Zinc and Lead Company's
mine at Shullsburg, I picked up a specimen of limestone
having a small cavity lined with pyrite crystals. Some of
the individuals have a diameter of two to three millimeters,
but the better crystals are seldom much over a millimeter in
diameter. They are usually combinations of the common
pentagonal dodecahedron (210) with the cube and octahe-
dron, and are but little distorted. Their habit is gener-
ally conditioned by the pyritohedron, which is generously
truncated by the cube and octahedron (plate 8, fig. 8). In
a few cases the pyritohedron is but little developed, the
form of the crystals being given by the cube. The faces
J System, 6th Ed., p. 95, fig. 4.
HOBBS MINERALOGY OF WISCONSIN. 145
are bright but have a purplish iridescence due to incipient
alteration. The pyritohedron was determined with suffi-
cient accuracy as the common form e, . (210) by meas-
uring the edge A on the reflecting goniometer, the result
obtained being 52 32', and the calculated value 53 8'.
Pyrite occurs at Mineral Point in cubes apparently un-
modified and as much as three-quarters of a centimeter on
an edge. Associated with these symmetrically developed
cubes are interesting groups composed of long columnar in-
dividuals arranged radially about a centre located a little be-
low the point of attachment (plate 8, fig. 9.). These crystals
have a length of a centimeter or a little less, and a thick-
ness of a little more than a millimeter. They are cubes
developed in the direction of one of the principal axes.
The individuals composing the group do not come in con-
tact, except perhaps at the point of attachment. Other
specimens from this locality are similar in character but of
much larger dimensions, the pyrite needles having a length
of several inches and a diameter of only a few millimeters.
The space between the pyrite needles is occupied by crys-
tallized sphalerite, which is in part coated with smithsonite.
The large radial sheaves of iron sulphide which occur at
Galena are for the most part pyrite.
A perfect unmodified octahedron of pyrite a half centi-
meter along the axes was collected by Mr. Cheney at Dem-
ocrat, near Etna, Wis.
AZURITE FROM MINERAL POINT.
Both the carbonates of copper are found at Mineral
Point attached to massive chalcopyrite, where they have
doubtless been formed through the action of carbonated
waters. The azurite is quite well crystallized, but the in-
dividuals are rarely over 2 ram long. In a few specimens
they attain dimensions of 3-4 ram The crystals have either
a domal habit with the ortho-diagonal the axis of great-
146 BULLETIN OP THE UNIVERSITY OF WISCONSIN.
est development, or a thick tabular habit with the basal
pinacoid the tabular face. Crystals of the first men-
tioned variety possess about the proportions given by Far-
rington for the crystals of lath-like habit from Arizona. 1
Different crystals show considerable variation in the oc-
currence of forms as well as in the relative development
of those which occur.
Three crystals have been completely measured, the first
two being lath-shaped, but representing different combina-
tions, and the third tabular. In all, ten forms have been
determined, four of which are new to the species.
On crystal I the prominent faces in the zone of the axis
& are the basal pinacoid, the negative unit orthodome
(tf), and the new form fPoo (205); and the crystal is
terminated by a single plane of e, |P2 (2 4 5). (See plate
7, fig. 6.) The habit of crystal II is conditioned chiefly
by the same forms as crystal I, with the addition of the new
form IP oo (203) in the zone of &; and though both e and
the new form b, IP! (9.12.8), are represented as terminal
planes, the former is much the larger, and one of its faces
is large and the other comparatively small (plate 7, fig. 7.).
On crystal III the terminal forms occur with their full
complement of faces, which have nearly equal development
(plate 7, fig. 8.). In addition there occurs on this crystal
a small positive hemi-brachypyramid, which has larger para-
meters on both c and a than has the form e. This pyramid
is not far removed from the zone of 245 and 245, but it
could not be accurately determined. An indeterminate
negative pyramid with much rounded faces and quite
small development, is also found on the crystal. This
crystal has as the largest faces in the principal zone,
the tabular basal pinacoid, the form 6 , Poo (TOl) and the
new form c, fPco (307). The only forms which are found
i O. C. Farrington, On Crystallized Axurite from Arizona. Amer. Jour. Sci. (3) XLI,
p. 300. (1891).
HOBBS MINERALOGY OF WISCONSIN. 147
on all of the three crystals are c, rf, e, and a. The new forms
lying in the principal zone were easily determined from
their angles with the basal pinacoid. The forms e and b
were determined, the former from its angle with c and
with 010 (one-half the angle e : e over the end of the ~b
axis), the latter from its angle with c and with both e
The forms observed on the three crystals are given
below, those that are new to the species being marked by
c, OP (001) I II III
a, ao Poo (100) I II III
*, Poo (101) I II III
c, --fPoo (307)* III
6, Poo (101) I III
b, IPoo (203)* II
n, iPoo (102) II
o, IPoo (205)* I II
6, iP2 (245) I II III
(9.12.8)* II III
The average of several measurements of the interfacial
angles of the planes of the above forms are given below.
The reflections from the pyramid faces are fairly good, but
in the principal zone the measurement is made difficult by
striation, particularly on the faces 6, a, and n, and by a
curvature, or better warping, apparently caused by the in-
tergrowth of nearly parallel individuals. This explains
the considerable variation between the readings of angles
and their calculated values, as indicated in the parallel col-
umns of the following table.
BULLETIN OF THE UNIVERSITY OF WISCONSIN.
The crystals are translucent with the beautiful azure
blue color characteristic of this mineral. They are some-
times coated with a thin film of green malachite.
MALACHITE FROM MINERAL POINT.
This mineral is found as a superficial alteration product of
chalcopyrite. Some very beautiful radial and sheaf-like
forms are to be seen in specimens in the University Collec-
tion. Some very minute crystals having a maximum length
of only about three-tenths of a millimeter, when examined
under low powers of the microscope appear as columnar
crystals much flattened in the plane of the ortho-pinacoid
(plate 7, fig. 5). This face is so much broader than the
others that the crystals invariably rest upon it and conse-
quently always exhibit parallel extinction. They are in all
cases bounded very sharply by the forms a, ooPoo (100);
m, ooP (110); c, OP (001); and 6, ooPoo (010); the latter plane
being very small and recognized only when the crystal is
HOBBS MINERALOGY OF WISCONSIN.
adjusted on the goniometer. Owing to the minute size of
the crystals, the face a is the only one which furnishes even
a fair image of the signal. The angle a : m was roughly
measured twice, using the front lens of the telescope, and
found to be about 39, the usual value given being 37 50'.
THE DRUSE MINERALS OF THE HAMILTON CEMENT ROCK
Calcite. The Hamilton cement rock which occurs at Mil-
waukee carries cavities in which good crystals of calcite 1
may be found. A number of specimens have been collected
by Professor Edward Kremers, the head of the School of
Pharmacy of the University , and generously presented to
the University Mineral Collection. I am therefore largely in-
debted to him for the material which is here described. The
crystals are translucent and either colorless or yellowish.
FIG. 9. CALCITE FROM MILWAUKEE.
They vary in length from 8-12 mm , and in diameter from
3-5 inm Their habit is short columnar, conditioned by the
combination of a steep positive rhombohedron and ^ R
(Oll2) (see figure 9). The former is much rounded but can be
approximately determined to be 18 R by measurement of
the convergence of the long sides of its faces. One crys-
tal in the collection was attached by this face and is doubly
1 The occurrence of calcite, pyrite, and rarely also sphalerite in the'cavities of the cement
rock has been mentioned by Chamberlin (Geology of Wisconsin, Vol. II, p. 393, 1878).
150 BULLETIN OF THE UNIVERSITY OP WISCONSIN.
terminated. The common scalenohedron R 3 , (2131) some-
times appears as a replacement of the solid angle formed
by two faces of i R and one of 18 R. The forms ob-
served are therefore
/>, 18R (220.127.116.11)
e t _R (0112)
v, R 3 (2131)
the two latter having been determined by the following
e : e, 0112 : 1102 44 35' 45 3'
v : v, (Y), 3121 : 2131 36 29 35 36
The faces are all somewhat rounded, particularly the
faces p and v. One specimen in the collection shows a
larger wine yellow calcite which is a parallel growth of
several simple rhombohedrons, about which and on which
the colorless crystals with habit pe have formed. This
larger crystal is thus shown to belong to an older genera-
FIG. 10. -PYRITE FROM MILWAUKEE.
Pyrite. The cavities in the Milwaukee Cement Rock
which contain the calcite crystals just described, are
often coated with pyrite, so that the calcite is formed on
the pyrite. The pyrite appears in good crystals having a
diameter of l-2' nm and is bounded by the octahedron and
cube. The habit is octahedral, the cube usually having a
small though a quite constant development (Fig. 10.).
Sphalerite. This mineral would seem to be much less
abundant in the cavities of the cement rock than either
calcite or pyrite. Only one specimen out of quite a num-
HOBBS MINERALOGY OF WISCONSIN. 151
ber supplied the writer by Dr. Kremers included any crys-
tals of sphalerite, and these were few and small. These
crystals were twinned according to the common law, as a
result of which they were flattened parallel to a face of
the tetrahedon. The faces are not bright enough for meas-
urement, but the forms Q (111), ocO (101). an icositetra-
hedron, and a hexoctahedron, can be made out upon them.
As is frequently observed on this mineral, the faces of
the tetrahedron show triangular markings. The faces of
the icositetrahedron truncate the edges of the hexoctahe-
dron, so that it is very probable that the icositetrahedron
is 2O2 and the hexoctahedron 3O|. In order to determine
with certainty, however, it would be necessary to secure
much better material.
Marcasite. While this paper was in the printer's hands,
I had an opportunity to visit the Milwaukee cement quar-
ries and collect there specimens of marcasite and celestite.
I also had an opportunity to make a hasty examination of
the valuable mineral collection owned by Howard Green,
Esq., in which are contained very beautiful millerite crys-
tals from the cement works. So far as I know, none of
these minerals have been reported from the locality.
The marcasite is found in very well formed, brightly iri-
descent crystals of lath-like habit, with the axis of devel-
opment the brachy-diagonal. The largest crystals found
had a length of only a few millimetres. The forms devel-
oped are apparently c, u, and ra, with other smaller faces.
They have not yet been carefully studied.
Celestite. This mineral occurs in masses as large as a
man's head composed of inter-grown crystals, the individ-
uals of which are sometimes several inches in length.
These masses are found in the layer of rock immediately
underlying the one quarried for cement. The crystals
seem quite pure and have a white color with irregular
areas of pale celestial blue. A qualitative determination
152 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
was made to identify the mineral. The powder of the
mineral moistened with hydrochloric acid yields in the
Bunsen flame the intense red color of strontium. Heated
on charcoal in the reducing flame of the blowpipe the min-
eral glows, and if fused with soda and placed upon moist-
ened silver, gives a deep stain of silver sulphide.
Hitlerite. Very beautiful specimens of millerite from the
cement quarries are contained in the collection of Mr.
Howard Green of Milwaukee. I have not yet found an op-
portunity to carefully examine them.
DIAMONDS FROM THE DRIFT.
Three large diamonds and a number of smaller ones
have been found in the glacial drift of Wisconsin. There is
also a report of three other diamonds, one of them as large
as a robin's egg, which were found and subsequently lost,
their real character not being known. It is not improba-
ble that the report is correct, but there is not sufficient
evidence to prove it. The large diamonds have all been
found in the " kettle moraine " outlining the Green Bay lobe
of the ice sheet, though the localities at which the finds
were made are somewhat widely separated. Several small
diamonds have been found in the bed of Plum Creek, Rock
Elm township, in Pierce county. The report on the Pierce
county diamonds has been made by Mr. George F. Kunz. 1
The writer has elsewhere 2 described the latest find at
Oregon in Dane county, and recorded facts furnished by
Col. S. B. Boynton of Chicago, concerning the finding of
the Eagle and Kohlsville diamonds. In the paper referred
to, the writer has also shown that the probable source of
the diamonds found in the Green Bay lobe of the "kettle
1 On the Occurrence of Diamonds in Wisconsin. Bull. Geol. Soc. Am., Vol. 2, p. 638.
Cf. also Min. Res. of U. S , 1889-90, p. 446. (1892.)
2 On a recent Diamond Find in Wisconsin and on the Probable Source of this and other
Wisconsin Diamonds. Am. Geol., Vol. XIV, p. 31-35. (1894.)
HOBBS MINERALOGY OF WISCONSIN.
moraine, is the region about the Menominee river in the
northeast portion of the state. At the time that paper was
written the Kohlsville stone had not been given an exam-
ination, but the writer has since had an opportunity to
examine it and has found it to very closely resemble the
other large diamonds found at Eagle and Oregon, so that
the theory that the diamonds found in the kettle moraine
have a common source, is thereby supported.
Below are given in tabular form the most important
facts concerning the recorded diamonds from Wisconsin.
Where and how found and by whom
Found by a laborer employed by Mrs.
Clarissa Wood, on farm owned (1876)
by Dr. Tucker and located in the
town of Eagle, Waukesha county.
Owned by Tiffany & Co.
Found by a small son of Charles De-
vine on farm of Judson Devine in
the town of Oregon. Dane county.
Owned by Tiffany & Co.
Found by a farmer. Louis Endlich,
while rolling a field on his farm at
Kohlsville, Washington county .
Owned by his widow, who now re-
sides at Kewaskum, Washington
Pierce County Diamonds.
Found by G. H. Nichols and party
while prospecting for gold in the
bed of Plum creek. Rock Elm town-
ship. Pierce county. Several of the
II, A. A
stones owned by Tiffany & Co.
It seems at first a little surprising that the Eagle and
Kohlsville diamonds should not have been earlier identified,
but it must be borne in mind that simple as is the
determination of this gem, it is rare to find anyone not a
professional mineralogist who would think to apply the
154 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
test of hardness. Experience seems to show that the aver-
age jeweler is as ignorant of the properties of the common
gems as is the farmer. Most people can with little trouble
have the use of either an emery wheel or a little coarse
emery, and since diamond is the only natural mineral which
can not be scratched by emery, no one need be without the
means of determining at once whether a rough stone is
EXPLANATION OF PLATES.
Crystals of calcite from southern Wisconsin,
Fig. 1. Crystal of type 1 bounded by R 8 and R and having much
rounded angles. Fig. 2a. Crystal of type 2a bounded by R 3 alone.
Fig. 2b. Crystal of type 2b bounded by |R and R. Fig. 3. Crystal
of the somewhat modified type 3. Excluding the small scalenohedrons
which bevel the edge re this crystal exhibits the following forms:
r,R; e,-|R; v, R 3 ; ft, ftR; *,-ifR; f,-2R; c, 24R; 5, 10R, k, fR.
Fig. 4. Crystal of type 4 which has the same modification as type 3 but
has rhombohedral instead of scalenohedral habit. Fig. 5. Twinned
crystal from the Linden mine with twinning plane the basal pinacoid.
The forms developed are R, R 3 , ^R, and OP. One of the individuals
has received a secondary growth of darker and yellow green calcite,
which tends to give symmetry of development to the twin. Fig. 6.
Crystal of type 6 bounded by the forms 24R, R 3 , $ R, and f R.
Calcite from southern Wisconsin.
Fig. 1. Parallel growth of calcites of types 1, 2a, 3, and 4.
Fig. 2. Stereographic projection of forms observed on calcites from
Galena from southern Wisconsin.
Fig 1. Large crystal from Yellowstone having an apparently hex-
agonal symmetry from development in the direction of a digonal axis.
HOBBS MINERALOGY OF WISCONSIN. 155
Fig. 5. Crystal from Yellowstone having apparently tetragonal sym-
metry from development in the direction of a principal axis. Figs. 3, 4,
5. Sections across a crystal of Galena from Yellowstone in the direction
of the cleavage. These sections show an interior core which is outlined
by a line of tarnish and includes irregularly shaped cavities. This core
is surrounded by a later growth which is polysynthetically twinned with
the twinning plane the rhombic dodecahedron. Fig. 6. Crystal of Ga-
lena from Mineral Point showing polysynthetic twin lamellae with the
twinning plane the rhombic dodecahedron. Fig. 7. Crystal of Galena
from Highland showing polysynthetic twin lamellae with the twinning
plane the octahedron.
Crystals of cerussite, barite, malachite, and azurite from southern
Fig. 1. Crystal of cerussite of type 1 from Highland. The forms
present are: i, 2Poo ; x, iPoo ; y \ 5 Poo*; p, P; 6, ocPoo ; m, ooP; and r, <xP3.
Fig. 2. Crystal of cerussite of type 2 from Highland. The forms pres-
ent are: p, P; m, ooP; a, ooPao ; 6, ooPoo ; , 2Pao ; fc, Poo ; and x, ^Poo.
Fig. 3. Twinned crystal of cerussite of type 3 with the twinning plane
the fundamental prism. The types present are: t, 2Poo ; or, |Poo ; m, ooP;
and p, P. Fig. 4. Crystal of barite from the Linden mine, bounded by
the forms c, OP; m, coP; and d, 4Poo . Fig. 5. Crystal of Malachite from
Mineral Point. Figs. 6 and 7. Crystals of Azurite of domal habit. Fig 8.
Crystal of azurite of thick tabular habit. The forms present on these
azurite crystals are: c, OP; a, ooPao ; tf, Poo ; c, f Poo *; 5, Poo ; b, f P oo*;
n, iPoo ; a, | Poo *, e, f P2; and b, -|P|*.
Crystals of marcasite and pi/rite from southern Wisconsin and Galena,
Fig. 1. Crystals of marcasite of type 1 which has thin tabular habit
and is bounded by the planes; OP, ooP, and Poo . Fig. la. Orthographic
projection on basal pinacoid of twinned crystal of type 1. Fig. 2. Lath-
shaped crystal of marcasite of type 2 bounded by the forms OP, ooPao ,
Poo , and ooP. Fig. 3. Stellate twin (cyclic fiveling) of marcasite, consti-
tuting type 3. Fig. 4. Crystal of marcasite of type 4, bounded only by
ocP and OP. Fig. 5. Crystal of marcasite of type 5 possessing pseudo-
156 BULLETIN OF THE UNIVERSITY OF WISCONSIN.
isometric habit, bounded by the forms Poo , Poo , ooP, P, and wPoo .
Fig. 5a. Orthographic projection of a polysynthetic trilling of marca-
site of type 5 on the basal pinacoid. Fig. 6. Twinned parallel growth
of marcasite of type 6 bounded by the forms ooP, Poo , and Poo . Fig. 6a.
Orthographic projection of marcasite trilling of type 6 on the basal pin-
acoid. Fig. 6b. Similar projection of simple twin of same type of mar-
casite. Fig. 7. Crystal of marcasite of pseudo-octahedral habit (type 7)
bounded by the forms Poo , Poo , OP, oo P, and P. Fig. 8. Crystal of pyrite
from Shullsburg. Fig. 9. Pyrite aggregate from Mineral Point.
Mineralogical Petrographical Laboratory,
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